There are many types of relay terminals, including relay terminals which are not capable of transmission, relay terminals with transmitting capability, and I/O relay terminals with, for example, photocoupler input and transistor output.
Since none of these existing relay terminals is capable of detecting relay failures (welding of contacts, faulty contacts, and so on) by themselves, faulty relays are slow to be detected. This delay leads to inconvenience, such as down time until a new relay can be installed.
To detect a faulty relay, one could use a logic circuit which has as its inputs the presence or absence of a load current from the relay and an output signal from the relay coil. Based on these inputs, the circuit could judge whether there were a relay fault. With this proposed circuit however, certain problems can occur:
(1) The range of load current which can be detected is limited; PA1 (2) There are limitations on the shape and dimensions of the current sensor; PA1 (3) It is difficult to provide adequate isolation between primary and secondary circuits and among the different poles; and PA1 (4) Such a device cannot be assembled efficiently. PA1 (1) The current flowing through a circuit flows through a coil so that it can be detected as a magnetic field by a magnetic-to-electric converter element. This scheme insures that the current in the coil will be detected reliably. Since this detection device is built into a relay terminal array, failures of relays can be detected reliably by a logic circuit; PA1 (2) The spatial relationship between the magnetic-to-electric converter element and the core is firmly fixed during assembly; PA1 (3) Sufficient isolation is provided between the primary and secondary elements; PA1 (4) The device can-be assembled efficiently. Since the case is composed of two symmetrical halves, it can be assembled merely by fitting two pieces together, a highly efficient mode of assembly; and PA1 (5) The configuration of this invention allows the unit to be assembled easily and enables it to be made more compact. PA1 (1) A logic circuit swiftly and reliably detects the failure of a relay based on the presence or absence of a current detected by the current detection unit, and on the on/off status of the relay. This allows a failure to be responded to quickly; PA1 (2) Each current detection unit, and indeed the entire device, is easy to assemble; PA1 (3) Since all components are arranged compactly, the terminal unit itself is compact; PA1 (4) The partitions in the spacer ensure that there is adequate isolation between different poles of adjacent current detection units; and PA1 (5) The partitions in the spacer prevent interference from external sources from reaching the current detection units.